Thats pretty interesting, I was wondering why I had such good Coralline growth and now I know why. I have only one fish and a handful of corals, My PH is constant on 8.4 and alkalinity is always high on about 10 - 12 dkh and I also have a strong water flow, this seems to all contribute to an enviroment prevered by coraline algae. I do not know how much phosphates have do with it but I can gaurantee you that mine are not at altra low levels.